1. Yes, you file one annual tax return and your businesses are reported on Schedule Cs included with that filing.
2. The United States taxes income "from whatever source derived." As an individual, all your income goes on one tax return: W-2, dividends, capital gains from shares of stock sold, loss form one side business, income from other side business. All of those items go on the tax return and drive the calculation of tax doe or refund coming your way.
